1. Field of the Invention
This invention relates generally to the manufacture of magnetic recording heads utilized in magnetic disk data storage devices and more particularly to a method for reducing damage to a magnetoresistive (MR) head during focused Ion Beam definition of the write head track width.
2. Description of the Related Art
Fixed disk data storage devices typically are magnetic disk devices which utilize a head disk assembly enclosed within a sealed volume with its associated electronics circuitry located adjacent, above or below the sealed head disk assembly or "HDA". The head disk assembly typically includes one or more planar disks stacked on a rotating hub of an included spindle drive motor. Each disk has a magnetic media on its upper and lower surfaces. One or more actuator assemblies for positioning magnetic transducers (heads) over the upper and lower surfaces of the disks is positioned adjacent the stack of disks and includes a rotary motor means such as a voice coil motor for rotating arms, which carry the heads, back and forth over the disk surfaces in order to read and write information from and to the disks.
Most of the conventional disk drives available today contain a single stack of disks and a single voice coil motor operated actuator assembly which utilizes a moving coil attached to the actuator itself. The actuator has the same number of heads as surfaces on the disks. The inner actuator arms typically carry two opposing heads, one for the lower surface of the disk immediately above and one for the upper surface of the immediately adjacent lower disk are. Actuator arms constantly being redesigned so as to be smaller and smaller in order to accommodate more and more disks in a given form factor.
There have been a number of attempts to increase the capacity of hard disk drives in other ways as well. One approach has been to increase the number of tracks on each disk surface. This requires making the tracks narrower, which inherently means that the write heads must be narrower, thinner and smaller. Also, as track widths gets narrower, interference between adjacent tracks during both read and write operations becomes a problem. One of the more innovative solutions which has led to smaller track widths has been the introduction of dual gap heads which utilize a separate gap for write operations and a separate gap containing a magnetoresistive (MR) element therein for read operations. These MR recording/read heads typically have three spaced pole tips forming two gaps, a write gap and a read gap. Separate gaps means that each can be optimized for its particular purpose, rather than representing a dimensional compromise.
The MR read/recording heads are formed on the trailing end surface of a slider block. The pole tip gaps are formed at the bottom edge of the trailing end surface of the slider block such that the tips face the media surface of the disk. The slider is in turn mounted on and carried at the end of an actuator arm which is positioned so that as the disk rotates, the slider floats on an air cushion, i.e., an air bearing film immediately above the media surface with the read/write pole tips as close as possible to the media without being in actual contact. The underside surface of the slider constitutes an air bearing surface for this purpose.
The head includes a top pole, a shared pole member commonly called the shared shield, and a bottom pole member commonly called the bottom shield. The latter two pole members are called shields because the magnetoresistive read element is placed in the gap between the shared shield and the bottom shield. These heads, commonly known as MR heads, are manufactured by photolithography techniques on an upper surface of a hard ceramic wafer, which later is cut into generally rectangular slider blocks with the upper surface of the wafer becoming the trailing end surface of the slider.
U.S. Pat. No. 5,314,596 describes the conventional wafer and slider bar processing steps. In general, a large number of MR heads are deposited on an upper planar surface of the wafer in a series of deposition steps involving depositing a series of alternating layers of a ferromagnetic flux conductive material, such as a nickel iron alloy (NiFe) and nonmagnetic electrically insulating material on the surface of the wafer. The conductive layers are each deposited as a thin film on the wafer planar surface. A photoresist is then deposited over the conductive thin film and a photolithographic mask is positioned over the photoresist covered wafer. The wafer is then exposed to light. This exposure causes the exposed areas of the photoresist to be resistant to chemical washing, in the case of a positive photoresist. In the case of a negative photoresist, the opposite occurs. In either case, the mask must be appropriate to the photoresist being used. After exposure to light, this mask is removed. The appropriate exposed or unexposed photoresist portions are washed away, depending on the type of photoresist used, leaving behind an exposed patterned surface of the conductive layer. A chemical etch process is then applied to the exposed conductive layer to remove the exposed patterned portions of the conductive layer. The remaining photoresist is then removed, leaving the desired pattern of conductor layer on the planar surface of the wafer. This patterned conductor layer defines the first pole of the head.
Next, an insulating layer is deposited and patterned in a similar manner as just described, and another conductive layer deposited. Then another photoresist is applied and another photolithographic mask positioned and the surface of the wafer again exposed to light. The mask is again removed and the unexposed photoresist portions washed away, leaving, exposed another patterned surface of resist and conductive layer. This process is repeated to complete the build up of the pole pieces and the coils for each of an array of identical heads on the planar surface of the wafer.
After the heads are formed on the upper surface of the wafer, the wafer is cut into strips or bars each containing a row of unseparated individual heads on one face thereof. The adjacent, orthogonal face of the bar on which the pole tips lie is defined as the air bearing surface and is shaped to provide the desired flying height characteristics of the head by lapping, sawing, ion etching, and/or ablative processes into the desired air bearing surface shape. The underside air bearing surface of the bar is then finally polished.
Next, the pole tips of each of the heads on each bar are trimmed by Focused Ion Beam (FIB) milling. This step is very critical to minimizing the write track width. Typically, the FIB milling step notches the pole tips to provide a precisely defined narrow width at the ends of each set of pole tips. This FIB notching, typically accomplished with a focused beam of positive ions, such as Gallium ions, ablates the pole tip material to produce the notched tips. The tips also must be accurately imaged and located prior to the milling operation. This preliminary imaging and locating step is also done with the focused ion beam. This preliminary step involves a short scan, but some of the ions may be implanted in the surface of the pole tip and some ablation of the tip occurs during this step as in the actual milling, operation. Therefore the time period for imaging and locating is kept very short to minimize this damage.
Once the tips are accurately imaged and located, the FIB mills the corners of the pole tips to define the precise width desired. During this FIB milling operation, some of the Gallium ions are embedded, i.e. implanted in the end surface of the pole tip, thus requiring a final lapping operation to remove these implanted ions and restore the desired magnetic characteristics of the NiFe pole tip material. This process is further described in U.S. patent application Ser. No. 08/982,542, allowed, Attorney Docket No. Q96-1046-US1 which is hereby incorporated by reference herein in its entirety.
A build up of electrical charge on the head surface also occurs during both the imaging and FIB milling operations since the focused beam is a beam of positive ions. Therefore a broad flood beam of electrons is supplied across the bar surface during the FIB etching process to neutralize this electrical charge. In actuality, though, the charge is not consistently and continually neutralized by this electron flood beam. In fact, surface charges build up and then dissipate over and over during the use of the focused ion beam.
Sometimes the charge builds up substantially and generates an arc when the charge discharges. These arcs are electrostatic discharges (ESD) and can damage the sensitive MR elements. Therefore there is a need for a method to eliminate the effects of ESD in order to increase the yield of good MR heads from the bars.
The FIBbed bars are cut into individual sliders and resistance checks performed on each slider after the FIB milling or etch process. A final lapping process is applied to each head that passes the resistance checks to achieve the desired final characteristics.
The failure rates mentioned above due to ESD damage have been acceptably low in the manufacture of anisotropic magnetoresistive (AMR) heads but substantially affect the cost of the final product. Further, ESD damage is prohibitively significant in the manufacture of Giant Magnetoresistive (GMR) heads. Therefore there is a need for a mechanism to eliminate these ESD failures in the manufacture of both AMR and GMR heads.